JP2904505B2 - Method of manufacturing steel wire for cold / warm forging and steel wire for cold / warm forging - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a steel wire for cold / warm forging which is used to finish a steel wire for machine structural use into a steel wire for cold or warm forging. The present invention relates to a manufacturing method and a steel wire for cold and warm forging.

(Conventional technology) For example, various bolts such as hexagon bolts, hexagon socket head bolts, U bolts, ball studs, and shafts manufactured by cold forging, and steel for machine structural use are usually S45C.S
A steel type consisting of Cr440, SCM435, etc. is used, and a steel wire that has been subjected to a predetermined heat treatment to a steel wire capable of meeting the extremely large plastic deformability required for the steel type is used as the material. However, other steel wire materials may also be used.

As the conventional cold forging steel wire of this type, there are known three types: a spheroidized annealed material, a coiled quenched material that is heat-treated in a coil shape, a tempered material, and a so-called non-heat treated material.

The spheroidized annealed material is manufactured by holding a coiled material wire made of a predetermined steel for machine structural use in an annealing furnace at, for example, about 700 ° C. for about 15 hours, and then spheroidizing the carbide in the slowly cooled steel. It has optimal mechanical properties for cold forging.

The coil-shaped quenched and tempered material is manufactured by heating and quenching a raw material wire made of a predetermined steel for machine construction in a coil shape in a furnace, and then heating and tempering the furnace. In addition, the wire can be used not only for cold forging but also for warm forging which is processed at a temperature lower than the tempering temperature.

The non-heat-treated material is a method for producing a martensite structure or a sorbite structure by directly quenching a wire from a high temperature state to a predetermined diameter by hot rolling.

(Problems existing in the prior art) Although the spheroidized annealed material is optimal for cold forging, the processing time for spheroidizing is long,
Since the material itself is expensive and must be subjected to quenching and tempering after forging, it is unavoidable that the cost will increase when the final product is formed, which is the greatest drawback.

On the other hand, since the non-heat treated material is manufactured by heat treatment following hot rolling, it is extremely inexpensive, but it is extremely difficult to finish the steel for machine structural use into a wire with large plastic deformability. It must be a low carbon steel and a special component system to which niobium, vanadium, etc. are added. Also,
The plastic deformability of the obtained wire is also limited, for example, JIS
If the bolt rating exceeds 8T, workability and impact characteristics will decrease. Further, there is a problem that the strength varies between lots.

The coil-shaped quenched and tempered material avoids the problems of the spheroidized annealed material and the non-heat treated material. That is, it is a steel for machine structural use, its processing time is much shorter than that of spheroidized annealed material, quenching and tempering after plastic working are unnecessary, and it is more excellent in plastic workability than non-heat treated material. In addition, warm forging is possible, and it is relatively inexpensive.

However, the coiled quenched and tempered material has a variation in strength in the length direction and the circumferential direction, and there is a risk of decarburization during furnace heating, and it is difficult to guarantee high quality and uniform quality. There are drawbacks. Since the uniformity of the wire quality is determined at the time of quenching and tempering, the above-mentioned drawbacks are not corrected, of course, even when subjected to warm forging.

(Object of the Invention) The present invention has been made in order to solve the above-mentioned problems in the conventional production methods, and uses a steel for machine structure as a material wire, and uses a conventional coiled quenching and tempering material. To provide a steel wire for cold and warm forging, which has a plastic deformability exceeding that of steel, has uniform quality in the entire length and circumferential direction, and can be manufactured in a short time and at low cost. Aim.

(Summary of the Invention) The gist of the present invention is as follows: (1) A material wire made of steel for machine structural use is rewound sequentially from a coil shape and allowed to run, and (2) The entire cross section is reduced from normal temperature within 60 seconds by a rapid heating means. The temperature is raised to a predetermined target temperature, immediately cooled, and the entire section is quenched. (3) Then, the temperature is raised to 600 ° C or more within 60 seconds by the rapid heating means.
The temperature is raised to a predetermined target temperature below the Ac ₁ shift point. (4) After maintaining the entire cross section at the above temperature for a predetermined time within a range of 0 to 600 seconds by a heat retaining device, (5) quenching. To manufacture a steel wire for cold and warm forging.

The steel wire obtained according to the above manufacturing method has a strength σb of 60 to 140
It is a steel wire for cold and warm forging with a Kgf / mm ² and a critical working ratio of 65% or more.

Further, the present invention resides in a method of manufacturing a steel wire for cold forging, characterized by subjecting the steel wire obtained by the above manufacturing method to (6) drawing.

Thus, the steel wire after drawing has a strength of σb60 to 140 kgf / mm
² , a steel wire for cold forging with a critical working ratio of 70% or more.

(Operation of the Invention) The configurations shown as the above (1) to (5) of the present invention exhibit the following effects.

Since the material wire made of steel for machine structural use is quenched and tempered in-line, heating and cooling are performed uniformly over the entire length and circumferential direction of the wire.

Since it is quenching consisting of rapid heating and rapid cooling of the entire section,
Since the crystal grain size of the wire is fine, rapid heating up to a predetermined temperature, and reliable holding of the entire cross-section at a constant temperature for a short time, uniformity of tempering is ensured.

The above operations are combined to obtain a finish in which the tensile properties of the wire are stabilized at a high level, the plastic deformation ability is large, and the deformation resistance is small. Also, since the residence time in the high-temperature region is short, decarburization does not occur.

Therefore, the obtained steel wire can be easily subjected to cold forging as it is to obtain a high-quality product, and further to hot forging at a temperature lower than the reheating temperature following quenching during production. If so, the mechanical properties and the metal structure are improved, but there is no deterioration, and a product having an extremely large plastic deformation can be obtained.

Further, when the obtained steel wire is further subjected to a drawing process, a further improvement in plastic deformability and an accuracy in diameter are weighted, and a finished dimensional accuracy is stabilized at a high level.

In other words, the present invention overcomes the disadvantages of conventional coiled quenching and tempering materials by providing in-line processing, quenching consisting of rapid heating and quenching, and rapid heating and reliable and short-term total cross-sectional isothermal holding. Another object of the present invention is to obtain a cold / warm forged material having high plastic deformability and homogeneity as well as improvement by a processing step characterized by tempering consisting of:

In addition, drawing improves plastic deformability, homogeneity and dimensional accuracy more.

(Embodiment 1) The present invention will be described in detail below with reference to an embodiment schematic diagram shown in FIG. The present invention can be applied to both solid and hollow materials as the material wire, and the wire diameter or the outer diameter is φ5.0 from the relation of the heating rate during heating described later.
The present invention is applied to a wire rod in a range from about 40.0 mm to about 40.0 mm. However, in this embodiment, the case where the material wire rod is a solid rod will be described.

In FIG. 1, 1 is a rewind stand, 2a and 2b are rapid heating means, 3a and 3b are rapid cooling means, 4 is an isothermal holding device, 5 is a take-up stand, 6 is a drive roll, and The coil-shaped raw material wire W made of steel for machine structure mounted on the vehicle is sequentially rewound by the drive roll 6 and travels at a predetermined speed in the direction of the arrow.

The wire W first passes through the rapid heating means 2a sequentially, during which the entire cross section is heated within 60 seconds from room temperature to a predetermined quenching target temperature determined according to the hardenability determined by the contained components. As the rapid heating means 2a, a direct-pass heating device or an induction heating device is used in view of the above-mentioned heating rate.

The heated wire W is quenched from all directions by the quenching means 3a provided continuously. The cooling fluid injected by the quenching means 3a is appropriately selected from water, quenching oil, a water-soluble polymer coolant solution or the like according to the hardenability of the wire.

The wire W then passes through the rapid heating means 2b, and the entire section is heated to a predetermined temperature within the range from 600 ° C. to the Ac ₁ transformation point within 60 seconds by the rapid heating means 2b, and immediately maintained at the same temperature. Head to device 4. As the rapid heating means 2b, a direct current heating device or an induction heating device is used in the same manner as the rapid heating means 2a because of the relationship between the heating rate.

While passing through the isothermal holding device 4, the wire W sent to the isothermal holding device 4 changes the entire cross section to the above temperature of 0 to 60.
The isothermal temperature is maintained for a predetermined time within a range of 0 second. The isothermal holding device 4 uses an electric heat radiation furnace, a hot gas atmosphere furnace, or an electric heating means to compensate the heat radiated from the surface of the wire W or the heat conduction to the core, so that the entire cross section has a predetermined temperature. Any type can be used as long as it can maintain the same temperature over time. Even if the traveling time of the traveling wire W through the inside of the isothermal holding device 4 is as short as 600 seconds or less, it is preferable from the viewpoint of decarburization prevention if the inside of the isothermal holding device 4 is an inactive region.

The reason why the present invention includes 0 seconds in the holding time range by the isothermal holding device 4 is that if the rapid heating means 2b is formed of an induction heating device, the induction heating device sets the surface of the wire W at a predetermined position. Although the temperature rises to the temperature, the temperature of the core portion has not yet reached the predetermined temperature at this time, so that the temperature of the surface side due to heat conduction in the isothermal holding device 4 until the time when the entire cross section is uniformly heated to the predetermined temperature. The decrease is supplemented, so that the soaking of the entire cross section is obtained, and the time when the soaking of the whole cross section is obtained is set to 0 second, and the holding time range is limited as described above from the relation of the finished strength. Things.

The wire W after passing through the isothermal holding device 4 is water, oil, water-soluble polymer coolant solution selected according to the hardenability of the wire,
Alternatively, it is quenched from the entire circumference by quenching means 3b capable of injecting a cooling gas or the like, and is sequentially taken up by the take-up stand 5.

The structure of the wire W obtained by the heat treatment step is tempered martensite over the entire cross section, and the tensile strength is a predetermined heating temperature within the range of 600 ° C. or higher to the Ac ₁ transformation point or lower by the rapid heating means 3b described above. Σb60 ~ 140Kgf / depending on holding time
It is finished within the range of mm ^2.

(Test Example: 1) In order to prove the performance of the steel wire of the present invention after the above heat treatment process, the present inventor carried out the method of the present invention on a 1 mm coil made of a S45C material having a diameter of 10 mm and applied it to a JIS standard 10T class. Finishing,
Various tests were performed. The test results are shown in Table 1 together with the test results of the conventional coiled quenched and tempered materials in which the same material and the same size wire rod were finished in the same class.

The tensile strength test and the decarburization test showing the stability of strength in the figure were performed according to the test method specified in JIS, and the deformation resistance test and the deformability test were performed according to the high-speed forging test standard.

From Table 1, it can be seen that the steel wire according to the present invention exhibits higher quality uniformity in cold forging than conventional coiled quenched and tempered materials, and has properties more suitable for cold forging. It is proved that.

(Experimental Example: 2) The inventor further carried out the method of the present invention on a SCM435 steel wire having a diameter of 11.2 mm to obtain a test piece, and investigated the performance of the steel wire of the present invention during warm forging. The specimens were heated at 580 qu.
℃ and 5sec, and finished at room temperature hardness of HRc: 39.

The processing experiments were carried out between 20 ° C (normal temperature) and 400 ° C and 500 ° C. The experimental results are shown in Table 2.

The table shows that the steel wire subjected to the method of the present invention has significantly reduced deformation resistance during warm forging, and a remarkable increase in the critical working ratio, and at the same time, maintains hardness at normal temperature. Thus, it was confirmed that the steel wire in which the method of the present invention was carried out was not only suitable for cold working but also for warm forging, and was most suitable for working with extremely large plastic deformation.

(Example: 2) The present invention includes a case where the steel wire subjected to the in-line heat treatment is further drawn. The drawing is for further improving the plastic workability between the examples of the steel wire for carrying out the method of the present invention and for adjusting the wire diameter.

The steel wire is drawn with a drawing die at a reduction in area of, for example, about 0 to 30%. Due to the drawing, the hardness of the steel wire hardly changes, and it becomes easier to process. In this case, the larger the reduction in area, the greater the difference between the hardness and the tensile strength, and as a result, it becomes easier to process for the tensile strength, but in reality, from the relationship with the tensile strength, The area reduction rate is naturally limited.

(Experimental Example: 2) Table 3 shows the results of an experiment in which the inventor of the present invention drew a steel wire that had been subjected to the method of the present invention at a reduction in area of 20%. The specimen is SAE10B3
5.Steel wire with wire diameter φ8.2mm.

From Table 3, it can be seen that, despite the same tensile strength before and after drawing, the drawn material has lower hardness and the Bauschinger effect is added, so that cold plastic workability is improved. It is proved that.

(Other Examples) In each of the above examples and experimental examples, a case where a steel wire for cold / warm forging processing is manufactured from a hot-rolled solid material wire has been described. The present invention is also applicable to a hollow material wire having a small diameter.

When it is necessary to descale the material wire, the descaler may be arranged at a predetermined position in the wire running line, for example, between the rewind stand 1 and the rapid heating device 2a.

It is needless to say that a lubricant for forging may be applied in the drawing process.

(Effects of the Invention) According to the present invention, it can be manufactured from steel for machine structural use similarly to the conventional coiled quenching and tempering materials.
Compared to tempered material, it has excellent uniformity of mechanical properties in the length direction and circumferential direction, has higher cold and warm plastic workability, and can obtain a steel wire with no decarburization. Up,
Processing time is much shorter than spheroidized annealing material,
Of course, quenching and tempering after cold or warm forging are unnecessary, so that the production cost of the final product can be reduced. Therefore, although the steel wire obtained by the method of the present invention is inexpensive, it is a steel wire material for cold and warm forging, which is much more suitable than conventional coiled quenched and tempered materials. It is highly evaluated and awarded as being, and the effect brought by the present invention is enormous.

[Brief description of the drawings]

 FIG. 1 is a front view showing an outline of an embodiment of the present invention.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) C21D 1 / 40,1 / 42,8 / 06 C21D 9 / 52,9 / 60,9 / 62

Claims (6)

(57) [Claims] 1. A material wire made of steel for machine structural use is rewound sequentially from a coil shape and run, while the entire cross section is heated from normal temperature to a predetermined target temperature within 60 seconds by a rapid heating means, and immediately quenched. The entire cross section is quenched and then heated to a predetermined target temperature of 600 ° C. or more and the Ac ₁ transformation point or less within 60 seconds by rapid heating means, and the entire cross section is heated to the above temperature within a range of 0 to 600 seconds by a heat retaining device. After holding for a predetermined time,
A method for producing a steel wire for cold and warm forging, characterized by quenching. 2. The method for producing a steel wire for cold and warm forging according to claim 1, wherein the element wire is a solid material or a hollow material. 3. The method for producing a steel wire for cold / warm forging according to claim 1, wherein the rapid heating means is an electric heating or an induction heating of the wire. 4. A raw material rod made of steel for machine structural use.
Strength σb60-140Kgf / mm obtained by applying the described process
^2, the cold limit working ratio of 65% or more, hot forging steel wire. 5. A method for producing a steel wire for cold forging, wherein the steel wire obtained by the production method according to claim 1 is subjected to a drawing step. 6. The method of claim denoted by an intensity σb60~140Kgf / mm ² obtained 5 wherein the step, limits processing rate of 70% or more of cold forging steel wire.